nz.co.gregs.dbvolution.annotations.DBForeignKey Maven / Gradle / Ivy
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package nz.co.gregs.dbvolution.annotations;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
import nz.co.gregs.dbvolution.DBRow;
/**
*
* Indicates that this field is a Foreign Key to another database table and
* specifies the table.
*
*
* public class MyTable extends DBRow {
*
* @DBColumn("other_table_fk")
* @DBForeignKey(OtherTable.class)
* public DBInteger otherTableFK = new DBInteger();
* }
*
*
*
* The class reference is to another DBRow class that represents the table of
* the foreign key.
*
*
* Multiple foreign keys to the same table can be handled by subclassing the
* original DBRow subclass. For instance Manager might be a trivial extension of
* the Employee class but it will be treated as a separate relation by
* DBvolution.
*
*
* DBForeignKey works with DBPrimaryKey and DBQuery to make Natural Joins happen
* automatically.
*
*
* DBForeignKey does not require a foreign key relationship to exist within the
* database and does not enforce referential integrity.
*
*
* DBForeignKey is generated automatically by DBTableClassGenerator if the
* foreign key is specified within the database.
*
*
Support DBvolution at
* Patreon
*
* @author Gregory Graham
* @see DBPrimaryKey
* @see DBColumn
*/
@Target({ElementType.FIELD, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
public @interface DBForeignKey {
/**
* Identifies the foreign table by its {@code DBRow} implementation class.
*
* Support DBvolution at
* Patreon
*
* @return the DBRow subclass that this foreign key references.
*/
Class value();
/**
* Identifies the foreign column by column name. This must be a column in the
* foreign class.
*
*
* If not specified, and the foreign class as exactly one primary key column,
* the primary key of the foreign class is used.
*
* Must be specified if the foreign class has no primary key, or if it has
* multiple primary key columns (not supported yet).
*
*
Support DBvolution at
* Patreon
*
* @return the name of the column this foreign key references.
*/
String column() default "";
}